1. Field of the Invention
The present invention relates to a positive type resist material with high oxygen plasma resistance and a process for forming high-resolution resist patterns.
2. Description of the Related Art
Recently, a single layer resist structure has been replaced by a multilayer resist structure to meet the requirement for forming high-resolution patterns. Bilayer and trilayer resist processes are discussed in "MULTILAYER STRATEGY FOR HIGH RESOLUTION LITHOGRAPHY" by C. H. Ting, I. Vigal and B. C. Lu, Intel Corporation, NVW Technology Development, pp. 139-149, CA 95051. Also, the trilayer resist process is discussed in "High-Resolution, Steep Profile, Resist Patterns", by J. M. Moran and D. Maydan, American Telephone and Telegraph Company, The Bell System Technical Journal Vol. 58, No. 5, May-June 1979, pp. 1027-1036. The bilayer resist process requires two photolithographic steps and the two resist layers tend to peel easily from each other. For this reason the trilayer resist process has been widely used.
In the trilayer resist structure, three layers are composed of a first resist layer for planarizing a wafer surface, a second resist layer consisting of inorganic film or metal film with plasma-resistance, and a third resist layer consisting of photo sensitive resist film. The third resist layer is firstly patterned by way of developing, the second resist layer is then patterned by using the third resist layer as a mask, and finally the first (bottom) resist layer is patterned by a method of reactive ion etching (R.I.E.) with the second and the third resist layers used as etching masks. These three layers are needed due to lack of photoactive resist materials which if used alone do not provide a sufficient oxygen plasma-resistance.
Therefore, the trilayer resist process has an advantage in forming high resolution patterns, but has disadvantages in its complexity and lower throughput.